If a software error corrupts a data object, or if erroneous data updates the data object, a data protection administrator may restore the data object to a previous uncorrupted state that does not include the corrupted or erroneous data. A backup application executes a backup operation either occasionally or continuously to enable this restoration, storing a copy of each desired data object state (such as the values of data and these values' embedding in a database's data structures) within dedicated backup files. When the data protection administrator decides to return the data object to a previous state, the data protection administrator specifies the desired previous state by identifying a desired point in time when the data object was in this state, and instructs the backup application to execute a restore operation to restore a copy of the corresponding backup files for that state to the data object.
A snapshot is a capture of a state of a data object, such as a file system or an application, at a specific moment in time. A file system may be stored on a storage array, which is a disk storage system that includes multiple disk drives. Unlike a disk enclosure, a storage array has cache memory and advanced functionality, such as virtualization and Redundant Array of Independent Disks (RAID). A data protection administrator may manage a backup application to create snapshots of data objects stored on multiple storage arrays.
In data transmission and data storage, a block is a sequence of bytes or bits having a fixed length, or block size. The process of putting data into blocks is used to facilitate the handling of a data-stream by a computer program receiving data. Blocked data is normally read a whole block at a time. Blocking is almost universally employed when storing data to 9-track magnetic tape, to rotating media such as floppy disks, hard disks, optical disks, and to NAND flash memory. Most file systems are based on a block device, which is a level of abstraction for the hardware responsible for storing and retrieving specified blocks of data, though the block size in file systems may be a multiple of the physical block size. In many file systems, a single block might contain only a part of a single file. Block storage is normally abstracted by a file system or database management system for use by applications and end users. An incremental block-based backup involves taking a snapshot of a file system, reading the blocks that have been modified since the last backup, and storing copies of the modified blocks into some block backed backup format, such as virtual hard disk (VHD).